1. Field of the Invention
This present invention relates to production equipment for oil wells and more particularly to removing a coupling from a sucker rod.
2. Description of the Related Art
Wells are drilled into the earth for extraction of oil. After a well is drilled, a metal casing is cemented into the wellbore to keep the hole from collapsing. The casing is punctured at the depth of the producing formation so that oil can flow into the casing. While oil from some wells flows to the surface due to high pressure in the earth, oil from some other wells must be pumped to the surface. In wells where oil flows under its own pressure, after the casing is cemented and perforated, a production tubing string is lowered to the perforation depth, a packer is set, and oil flows through the production tubing string. In the case where oil does not flow under its own pressure, the production tubing string is lowered to a predetermined depth and secured by a tubing anchor. A well head secures the top of the production tubing string. A pump is attached to a sucker rod and lowered into the well by attaching one sucker rod after another using a coupling for each connection. A series of sucker rods connects the pump to surface equipment that moves the entire length of sucker rods up and down to provide a reciprocating motion for the pump, which pumps oil up through the production tubing string around the sucker rods.
Each sucker rod is typically a cylindrical bar of metal that has male threads on each end. The length of the rods ranges between about 25 and about 30 feet, and the diameter is typically ½, ¾, ⅞, ⅞ EL, 1 or 1 and ⅛ inches. The rods are connected end to end by a coupling, which is often referred to as a box. The coupling or box is a hollow cylinder having an inside wall that is threaded, which are referred to as female threads, for engaging the male-threaded end of a first sucker rod and the male-threaded end of a second sucker rod, which fastens or couples the first and second rods together in an end-to-end fashion. Sucker rods are connected together by couplings to extend thousands of feet down into a well for reciprocating a pump at the bottom of the length of rods for pumping oil to the surface. The couplings have a greater diameter than the rods, and the couplings tend to wear as they rub against the inside wall of the production tubing string.
For maintenance and repair, the sucker rods and pump are pulled out of the well from time to time. A workover rig is installed over the well, and the sucker rods are hoisted upwards a pull-length at a time and held in place while the length of rod pulled out of the well is removed from rod below by loosening a coupling connection. Loosening the coupling is often called breaking the joint. The length of rod pulled up and out of the well each time may be as much as three individual sucker rods, so not every coupling connection is broken loose from the two rods that are joined by the coupling. The lengths of rod are kept in order for reassembly and lowering back into the well in the same order.
A tool called a power sucker rod tong is used for coupling and de-coupling the rods with the couplings, which is referred to as making and breaking the joints. Power sucker rod tongs were developed many years ago, and U.S. Pat. No. 3,144,794, issued to Foster and incorporated by reference, provides a description of one such example. U.S. Pat. No. 6,374,706, issued to Newman on Apr. 23, 2002, and incorporated by reference, provides a more recent example of a power sucker rod tool. To understand how the sucker rod tool works, a more detailed description of the sucker rods is needed. An end of a sucker rod is cylindrical and has 2 or 3 or so inches of male threads at each end, which is referred to as a pin. A cylindrical shoulder protrudes radially from the rod at the base of the pin, and the shoulder is adapted to abut against an end of a coupling. Spaced immediately inwardly from the shoulder is a drive head that is typically square in cross-section, which provides opposing flat surfaces. The opposing flat surfaces, which are referred to as flats, can be engaged by an open-ended wrench sized to engage the flat surfaces. Sucker rod tongs have such an open-ended wrench, referred to as a backup wrench, for engaging the flats and holding the sucker rod to prevent rotation.
After a pull-length of sucker rod is pulled out of a well, the rod is held in place near the surface of the earth to keep it from falling into the well. Power sucker rod tongs are pulled manually into engagement with the sucker rod at a coupling. The backup wrench engages the flats of a rod below the coupling, and a carrier jaw in the tongs engage the flats of the rod above the coupling. Powered by a hydraulic fluid, the carrier jaw rotates to loosen either the rod above the coupling or the rod below the coupling from the coupling. Depending on which connection breaks loose, the coupling either stays on the rod above the coupling or on the rod below the coupling. The rod above the coupling is set aside in the order of withdrawal from the well so that during reassembly, the rod above the coupling, the coupling and the rod below the coupling mate properly.
Some of the couplings or boxes need to be replaced due to wear from sliding up and down inside the tubing or due to a concern that the coupling may fail after being placed back in service, such as due to a crack in the coupling. Couplings have been typically removed manually from the sucker rod on which the coupling remains after use of the power sucker rod tool. Manual removal often involves striking the coupling with a hammer to loosen the threads, which carries a risk of injury from the hammer glancing off and hitting someone. The couplings are made of a hardened steel that can chip or even burst under certain stresses imparted by twisting and hammering on the coupling, which can result in emitting a shard of metal that may become embedded in a person's body or eye. A pipe wrench may be used on the smooth, cylindrical coupling, but the hardened metal prevents the wrench from biting into the metal for a good grip, resulting in slippage that can cause injury. So much torque is required to break the threads loose that a pipe is often placed over the end of the pipe wrench for additional leverage. If the wrench slips suddenly, there is a risk of injury to the person or persons pulling or pushing on the pipe wrench and its extension, as well as a risk to other people working on the task. In addition to the risk of injury imposed, removing couplings from sucker rods is a labor-intensive and time-consuming process.
Inventors have developed tools for breaking a coupling loose from a sucker rod. U.S. Pat. No. 5,361,831, issued to Young, describes a rod coupling breakout device, which provides a cylindrical housing that fits over a coupling. A pair of opposed impact transmitting members pass through the housing. A hammer can be used to strike the impact transmitting members to loosen the threads, and in the event of a catastrophic failure of the coupling, the housing contains any shards that would otherwise have been emitted.
U.S. Pat. No. 5,010,635, issued to Clark, describes a sucker rod coupling breaking tool. A first, preferably stationary or non-rotatable, wrench is provided with a coupling engaging clamp apparatus that has a plurality of jaws or clamp members that that circumferentially extend about and encapsulate a coupling to hold it and prevent rotation. A second wrench is open ended and adapted to engage the square, flat portion of a sucker rod. The second wrench rotates the sucker rod while the first wrench holds the coupling, which unscrews the coupling from the sucker rod.
U.S. Pat. No. 5,433,128, issued to Wacker, describes a sucker rod coupling tool for either breaking or tightening the threaded joint between a sucker rod and a coupling. The tool has a friction wrench that engages the outside of the cylindrical coupling and a backup wrench that engages the square flats of the sucker rod. The backup wrench is stationary, and the friction wrench rotates the coupling to break the threads loose or to tighten them.
U.S. Pat. No. 6,942,254, issued to Cartsensen and incorporated by reference, describes another variation on a tool for making or breaking connections between a coupling and the pin end of a sucker rod. Several jaws move radially inwardly to clamp the coupling into a fixed position, and a wrench engages the square flats adjacent the pin end of the sucker rod. The wrench rotates while the jaws hold the coupling stationary to loosen or tighten the threaded joint.
Although there have been a number of advancements in this art, there remains a need for a tool that is convenient and easy to use. The tools described in the patents above may work quite well, but they are not typically being used in the field as sucker rod is removed from a well bore. When a coupling needs to be replaced, it is still generally done manually with hammers and pipe wrenches as described above. Thus, there remains a need for a tool for breaking the threaded joint between a coupling and a sucker rod that reduces the time required for this task and makes the task safer to perform.